1. Field
The field of the present invention relates to particle beam lithography and, in particular, to combining and shaping cell patterns for improved particle beam efficiency.
2. Description of Related Art
In today's semiconductor manufacturing process, a common approach, as shown in FIG. 1, is the use of photo-lithography machines 10 and photo-lithography masks 12. In general, the mask 12 has an image for a layer of a chip that, through a series of lenses 14, is projected onto a wafer 16. Multiple chip images 18 are formed on the wafer 16 by stepping and repeating the mask image process across the surface of a wafer 16. The mask process is relatively fast, taking approximately one to five minutes per layer. Current dies typically comprise about 30 layers. Some precision layers require more than one mask per layer. The mask set is highly expensive, costing about 2 million dollars for a 90 nm design, and about 3 million dollars for a 65 nm design in the initial year of production. Further, it is time-consuming to produce the mask sets, requiring about a month turnaround time for creation, validation and repair. In addition, mask use is troublesome, since the use of light reaches physical limitations that have to be accounted for in some manner as the device sizes decrease, i.e., light becomes too coarse of an instrument as the design size shrinks.
One approach that overcomes some of the problems associated with the use of photo-lithography based manufacturing is the e-beam direct write method that employs an electron beam to write directly on a wafer. Cost is reduced significantly since no mask is required. Further, the use of the e-beam can handle device sizes down well below 45 nm. However, since the process is not a step and repeat procedure, it takes a long time, e.g., on the order of ten hours for the many data intensive layers. In general, this amount of time is impractical for providing efficient production of mass chip quantities. Thus, a need exists for a manner of making e-beam efficient enough to be used in mass production.